将语言环境更改为 en_US.UTF-8 但程序仍尝试翻译成其他语言

我将系统区域设置更改为en_US.UTF-8with dpkg-reconfigure locales。locale命令输出：

LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

在/etc/default/locale我有以下内容：

LANG=en_US.UTF-8

此外，/etc/locale.gen确实只包含en_US.UTF-8 UTF-8.

unattended-upgrades每天早上运行从/etc/cron.daily/apt-compat在我的系统日志中产生以下错误：

apt.systemd.daily[3829]: --- Logging error ---
apt.systemd.daily[3829]: Traceback (most recent call last):
apt.systemd.daily[3829]:   File "/usr/lib/python3.5/logging/__init__.py", line 983, in emit
apt.systemd.daily[3829]:     stream.write(msg)
apt.systemd.daily[3829]: UnicodeEncodeError: 'ascii' codec can't encode character '\xfc' in position 43: ordinal not in range(128)
apt.systemd.daily[3829]: Call stack:
apt.systemd.daily[3829]:   File "/usr/bin/unattended-upgrade", line 1538, in <module>
apt.systemd.daily[3829]:     main(options)
apt.systemd.daily[3829]:   File "/usr/bin/unattended-upgrade", line 1219, in main
apt.systemd.daily[3829]:     logging.info(_("Allowed origins are: %s"), allowed_origins)
apt.systemd.daily[3829]: Message: 'erlaubte Urspr\xfcnge sind: %s'
apt.systemd.daily[3829]: Arguments: (['origin=Debian,codename=stretch,label=Debian-Security'],)

系统试图翻译Allowed origins are: %s成德语版本erlaubte Ursprünge sind: %s，其中包含一个特殊的字符ü。经过一番研究，我发现带有翻译的文件可以在这里找到：/usr/share/locale/de/LC_MESSAGES/unattended-upgrades.mo.

为什么apt/unattended-upgrades尝试将英语翻译成德语，因为我已经将语言环境更改为正确的英语值？我怎样才能阻止这种行为？